Add all Shape skeleton classes.

shapefile_parser/shapefile.py
	-Add skeleton classes for all shapefile shape-types
	(`NullShape`, `PolyLines`, etc.).
	-Add complete `__init__` definitions for all shape-types in
	"x, y space" (not "measured" or "x, y, z").
Add full Point class implementation.

shapefile_parser/parser.py
	-Remove existing shape class implementations, because they
	were incomplete (see next point).
	-Redefine the `Point` class with full documentation; add
	`Point.read_from_binary_string()` and
	`Point.write_to_binary_string()`.
Add MultiPoint class implementation.

shapefile_parser/shapefile.py
	-Add full, documented `MultiPoint` implementation, with
	`MultiPoint.read_from_binary_string()` and
	`MultiPoint.write_to_binary_string()`.